Symbolism, Imagery, Allegory
What a load of bull. Er—what a load of bulls. There are just so many bulls rushing around this novel.
Bulls and bull-fighting are the two most critical symbols in The Sun Also Rises. The bulls symbolize passion, physicality, energy, and freedom. If that's not enough symbolic weight for these poor little boy-cows (not cowboys), in the bulls' interactions with the bull-fighters, they also come to symbolize the act of sex. Each bull-fight involves seduction, manipulation, maneuvering, and penetration by the bull-fighter of the bull. Yowza.
It is significant that, of all the characters, Jake, Brett, Romero, and Montoya are the most stirred by bull-fighting.
Romero’s status as bull-fighter suggests that, unlike the novel’s other male characters, he is capable of passionate love and sex. Although Cohn clings to an illusion of love for Brett, he is repelled initially by the bull-fights as boring, then later as gruesome. These means, in the more-than-slightly messed up world that Hemingway has created, that he's not a manly man.
Brett is undisturbed by the gore of the bull-fights and, like Jake, is entranced by the interaction between bull-fighter and bull. After watching the bull-fights, Brett is determined to be with Romero. Brett digs a man in tight green pants who kills animals.
Jake, it seems, strives to experience sensuality vicariously through the bull-fights (as he is unable to have sex himself). As an aficionado, Jake recognizes and loves the passion of bull-fighting, suggesting that he, too, is a passionate man. Jake’s knowledge of bull-fighting empowers him to authoritatively describe the bull-fights to Brett.
Although we don't learn much about Montoya’s personal life, it is apparent that he views bull-fighting as the highest, purest art form, one that exceeds all else in love, beauty, and passion:
Montoya could forgive anything of a bull-fighter who had aficion. He could forgive attacks of nerves, panic, bad unexplainable actions, all sorts of lapses. For one who had aficion he could forgive anything. At once he forgave me for all of my friends. Without his ever saying anything they were simply a little something shameful between us, like the spilling open of the horses in bull-fighting. (13.24)
As discussed briefly in the our character analyses, the bull-fights can also be read as paralleling the characters and events of the novel. During the running of the bulls, to take just one example, a man is gored and killed the same day that Cohn leaves Pamplona—that dude is a crushed and dead on the outside as poor Cohn is on the inside.